Field of the Invention (Technical Field)
The present invention is related to fabrication, assembly, feature integration and operation of low cost, flexible, high performance radiation detectors based on thin, singulated, flexible semiconductor devices and necessary functionalization materials.
Background Art
Note that the following discussion may refer to a number of publications and references. Discussion of such publications herein is given for more complete background of the scientific principles and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Radiation detection is a critical function for a very large variety of applications, ranging from biomedical, to homeland defense, military, environmental monitoring, disaster response and natural resource mapping and many others. Legacy radiation detectors have relied on very well established methods and instruments for detection of high energy photons (gamma, x-ray), alpha, beta or neutron particles, as well as protons, and heavy and light nuclei. Such legacy detectors include gas detectors that rely on the ionization of the detector gas to detect the incident alpha, beta or gamma or neutron radiation, including Geiger-Mueller detectors, proportional counters, He-3 tubes for neutron detection, cloud chambers for heavy nuclei detection, and many other configurations. Another class of radiation detectors consists of scintillation detectors where the incoming radiation interacts with detector material that produces light (in some cases electrons) as a result of the interaction. The light produced in this interaction may or may not be proportional to the energy of the incident radiation, but is typically at least proportional to the intensity of the incident radiation. The light produced from this interaction in a scintillation detector is captured by a light capture detector, such as a photo-multiplier tube, or a photodiode, for example. In other instances, the radiation is detected with a solid state material where the interaction of the radiation with the detector produces electron-hole pairs that are swept into the electrodes connected to the detector material to produce an electronic pulse of different magnitude depending on the number of electron-hole pairs that the interaction has produced.
The gas detectors can be made specifically to detect different types of radiation by selection of the fill gas, thickness of the detector “window” through which the radiation reaches the detector volume, and the operating voltage. Typically, gas detectors cannot differentiate between the energies of the incident radiation. They can be used to detect the presence or absence of the type of radiation they are designed to measure and/or to measure the intensity of such radiation present. Gas detectors are typically operated at ambient temperature. Scintillation detectors typically provide a light signal that is proportional to the energy of the incoming radiation, as well as being proportional to the intensity of the incident radiation. For some scintillation materials, e.g., plastic scintillators, the energy resolution is minimal. For others, such as NaI or CsI, the detectors are classified as medium resolution detectors. Scintillation detectors are also typically operated at ambient temperature. Solid state detectors provide a direct electronic signal that is proportional to both the energy of the incident radiation and the intensity of the incident radiation. Solid state detectors are generally classified to be high energy resolution detectors. They range from silicon detectors for alpha and beta measurements to CdTe detectors (neither of which requires cooling) to Ge detectors that are cooled to liquid nitrogen temperature for proper operation.
Each of these detector types have weaknesses and limitations. Gas detectors have little stopping power to see higher energy gammas, and saturate easily without special electronic circuitry and tricks. It is difficult to automate the manufacturing of gas detectors, which keeps the detector prices high. Scintillation detectors have good stopping power, but are very heavy being large detectors, difficult to handle, cannot take rough handling, and are expensive. CdTe detectors simply cannot be made in large size; if a large detector active size is required, one must use arrays of the detectors which is both expensive and requires duplication of the electronics adding to the complications and expense. HPGe detectors have the ultimate energy resolution but require cooling mechanisms (liquid nitrogen dewars or mechanical cooling systems), which makes them both expensive and bulky. They also cannot be made arbitrarily large. Furthermore, many of these systems are bulky, require integration and careful handling of fragile and/or hazardous materials and some systems also require cryogenic cooling to achieve the desired functionality.